Liquid crystal display (LCD) technology, wherein a backlight is selectively transmitted through an array of pixels each comprising three or more individually controllable color filters, is a dominant means for displaying electronic images. LCD devices have inherent design tradeoffs, including those involving brightness, color gamut, contrast, and power consumption. Filters with narrower wavelength bandwidth provide more saturated colors but admit less light, causing brightness and luminous efficacy to suffer. Increasing filter wavelength bandwidth increases brightness but reduces color gamut. Increasing backlight intensity improves display brightness but increases power consumption and reduces contrast, since LCD filters cannot reduce their transmittance to zero. Traditionally LCD backlights have employed fluorescent lamps, with phosphors chosen in concert with the color filter material. The cost, availability, and characteristics of these physical materials largely constrain LCD design options.
Light-emitting diode (LED) backlight technology is now being used for improved LCD designs. The spectral transmittance of real-world color filters overlap, but the narrow bandwidth of LED emitters can be used to avoid producing light energy in these spectral regions and thus reduce crosstalk among the color components. Another recent improvement is local dimming, wherein the display's pixel array is divided into segments, each lit by an independently-controlled LED backlight whose intensity is adjusted according to the image brightness of its portion of the overall image. The color filters inherently waste energy by blocking light, but local dimming allows the filters to operate at a higher average transmittance, reducing power consumption while increasing contrast. The combination is beneficial because it combines the economical high-resolution of LCD filters with the easy controllability of LED emitters. Unfortunately this approach does not improve the tradeoff between color gamut and luminous efficacy. Producing saturated colors requires light limited to a narrow portion of the visible spectrum. To the extent that the required spectral energy of the image does not match the available spectral energy of the backlight, the color filters must block—and thus waste—considerable amounts of light. What is needed is a better match between backlight spectral energy and the displayed image.